Exemplary embodiments of the present invention relate to a connection structure.
German patent document DE 10 2004 018 977 A1 discloses a generic type of connection structure. An under body construction of a motor vehicle is described therein, which has diagonal struts for stiffening. The struts are provided with screw holes at their ends and accordingly are screwed onto the vehicle under body.
In order to achieve lightweight construction the use of fiber-reinforced plastics (FRP) is conceivable. However, problems arise in the use of screwed connections with regard to the setting behavior of the plastic, since this leads to preloading losses. Furthermore, the orientation of the fibers is disrupted and broken due to the screw holes and hence the struts are weakened.
Exemplary embodiments of the present invention are directed to a connection structure in which a first component made of a lightweight construction material with a minimum possible weight, while at the same time having a high stiffness, can be connected with process and operating safety with a second component made of a steel material.
Exemplary embodiments of the present invention employ an intermediate component that facilitates the connection of the two components, in that the first component, which is made of FRP, forms a non-detachable plug-in connection with this intermediate component, which avoids a direct screw connection of the first component with the second component. Accordingly, the setting behavior of the FRP is no longer a concern and the orientation of the fibers is not disrupted or completely broken due to a processing operation, such as drilling, cutting, etc., which is required in the provision of openings. Other potential related damage caused by delamination of the FRP is also prevented. On the basis of the choice of a metallic material, preferably a ferrous material for the intermediate component, a connection to the second component, which consists of a steel material, is relatively simply executed. The use of an FRP material for the first component provides a desired light construction with minimum possible weight and good stiffness. The plug connection is fast, light and is accomplished with process reliability. It is also reliable operationally, even under high mechanical stress. Accordingly, exemplary embodiments of the present invention provide a connection structure for FRP components that is simple to execute and consists of reasonably priced materials, thus favoring a decision for its use in the installation of FRP components in series production. In addition, the manufacture of the connection structure is very satisfactory with regard to assembly considerations, since the FRP component can be delivered with the intermediate component as a pre-assembled module, i.e. delivered in non-detachable connection to then be fixed to the second component.
The intermediate component is preferably formed on one end with a mounting flange, by means of which the intermediate component can be simply and easily joined to the second component. To this end all customary jointing techniques can be advantageously employed. For example, the use of adhesives/bonding, welding, soldering, clinching and even clipping are conceivable. The flange can simply be formed with an opening, such that the intermediate component and—indirectly—also the first component can be screwed to the second component. In particular, the shape of the flange can be matched to the contour of the second component, so that even in the case of more complex component contours, a secure fixing of the intermediate component and the first component to the second component is possible without problem.
The intermediate component can be a forging, casting, machined component-milled or turned. However, preferably the intermediate component is formed as a sleeve with a flattened end. The sleeve can take the form of a section of tube, whose profile is squeezed flat at the end to form a fixing flange. For its manufacture it is conceivable to process the section of tube by means of an internal high pressure forming process, whereby first an optimum cross-section adaptation to the plug-in connection for the first component can be achieved. Second, it is possible to sequence the squeezing process in the same tool as used for the internal high pressure forming process. For this purpose it is merely necessary to integrate appropriate stamps in the tool. It is also possible to execute the squeezing through the tool itself in the course of the closing operation of the tool. Furthermore, the formation of screw openings in the same tool is possible, in which stamping punches are used, which are likewise arranged in the tool.
Particularly preferred is the non-detachable plug-in connection, in the form of an interference fit and/or by means of a layer of adhesive. The interference fit can be achieved by pressing the press-in part of one component into the receptacle of the other component, or by the shrinking of one plug-in partner after it has been fitted onto the other in an initial clearance fit. In the latter technique the metallic intermediate component is very considerably cooled, at least on its end providing the plug-in connection, followed by a sliding together of the two components of the joint, after which the connection is heated up and the interference fit is obtained as a consequence of the expansion of the material of the intermediate component.
Alternatively or additionally, the non-detachable connection can also be formed by an adhesive layer. In this case the receiving end and/or the end of the plug-in partner to be received is/are first coated with a layer of adhesive. The adhesive layer can be moist, and hardens on the sliding together of the layers. However, the adhesive layer can also first be dry and inactive and then activated on the sliding together of the surfaces to be jointed and the application of radiation, triggering their adhesive properties, finally resulting in hardening. An outlet channel to allow for possible overflow of the adhesive is provided in the intermediate component.
Particularly preferred are plug-connected ends of the first component and the intermediate component with extensive separation between them by means of an electrical insulating element extending over the length of the plug connection. This prevents contact corrosion of the steel material of the second component and, if necessary, of the metallic intermediate component. This corrosion is caused due to a relatively large difference in the electrochemical potentials of the first component and the second component and to that of the intermediate component of the connection structure. The electrical insulating element can preferably be an adhesive layer and/or a winding of glass or aramide fiber-reinforced plastic, i.e. a relatively base FRP. The use of the adhesive layer simultaneously provides a non-detachable connection with simple constructional means while also preventing contact corrosion.
The prevention of contact corrosion is particularly important if the first component is made from carbon fiber-reinforced plastic (CFRP), which is a particularly precious material. Additionally, the connection structure according to the invention is important for this material, since the manufactured first component has to carry high mechanical loadings and for this purpose is provided with a unidirectional fiber orientation. In the CFRP material the fiber orientation would be seriously distorted by connection openings and the component would not be usable for the intended application. The connection structure has also been shown to be corrosion resistant to road salt and stone chippings.
Although in the framework of the invention the range of applications of the connection structure is very wide and also associated with aircraft construction, it is particularly preferred that the first component forms a framework structure component, a strut or a supporting component of a motor vehicle, while the second component forms a vehicle body component adjoining or close to the first component. In this respect the application of FRP, preferably CFRP for the lightweight construction of motor vehicles and the associated reduction in emissions and fuel consumption.